In many electrical circuits, there is a need to combine two or more signals to produce a signal based on the input signals. The process of combining two or more signals to produce a new signal based on the input signals can be broadly referred to as aggregation. In some cases it is desirable to combine two or more signals and obtain an average signal. For example, in thermal processing equipment, it may be desirable to use more than one temperature sensor and to average the readings in order to get a more representative value.
FIG. 1 is a prior art averaging circuit 100. The averaging circuit includes a first stage 102 and a second stage 104. The first stage 102 includes three inputs 106 that are coupled through three resistors 108 to an inverting input 110 of a first operational amplifier 112. A non-inverting input 114 of the first operational amplifier 112 is grounded. A feedback resistor 116 is coupled between an output 118 of the first operational amplifier 112 and the inverting input 110. The first stage 102 outputs an inverted average of the signals applied to the three inputs 106. The second stage comprises a fourth resistor 120 coupled between the output 118 of the first operational amplifier 112 an inverting input 122 of a second operational amplifier 124. A non-inverting input 126 of the second operational amplifier 124 is grounded. Another feedback resistor 128 couples an output 130 of the second operational amplifier 124 to the inverting input 122 of the second operational amplifier 124. Thus, the second stage 104 forms a unity gain inverting amplifier. The second stage 104 inverts the inverted average to produce the average.
FIG. 2 is a surface plot 200 of the average function. In FIGS. 2, 4 and 6 the independent variable axes labeled X and Y represent circuit inputs (note this is for the case of two inputs) and the value of the dependent variable (denote as Z in the plot 200) is the output of the circuit.
In some technical applications rather than an average of two signals, what is needed is the maximum of the two signals. For example in certain types of thermal processing it is more important to control the maximum temperature in order to avoid damaging work in progress.
FIG. 3 is a prior art MAX function circuit 300. The circuit 300 comprises a first input 302 coupled through a resistor 304 to an inverting input 306 of an operational amplifier 308. A second input 310 of the circuit 300 is coupled to a non-inverting input 312 of the operational amplifier 308. A forward biased diode 314 is coupled between an output 316 of the operational amplifier 308 and the inverting input 306. The signal produced at the output 316 is written in mathematical notation as MAX(V1, V2) with V1 and V2 denoting the signals applied at the inputs 302, 310. FIG. 4 is a surface plot 400 of the MAX function.
In yet other types of systems, a circuit that produces a signal that is equal to the minimum of two circuits is needed. For example in certain thermal reactors it is important to have a signal representative of a minimum temperature in order to make sure that all areas of a material undergoing thermal processing have been subjected to at least a minimum specified thermal processing.
FIG. 5 is MIN function circuit 500. The MIN function circuit 500 differs from the MAX function circuit 300 in that the direction of the diode 514 is reversed. FIG. 6 is surface plot of the MIN function.
For certain complicated systems such as complex signal processing or control systems it may not be known ahead of time how two signals should be combined at one more stages within the systems. In these cases it would be desirable to provide a reconfigurable signal aggregator. It may be advantageous to allow an operator to reconfigure the signal aggregator or in some cases machine learning can be used to automatically determine an optimal configuration of the signal aggregator.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.